Effects of mineral additives and age on microstructure evolution and durability properties of sand-reinforced cementitious mine backfills

Abstract

Cementitious paste/mine backfill (CMB/CPB) is a creative way to proficiently decrease the sum of sulfidic tailings. However, considering them as minor raw material and inadequacies in their gradation, OPC (costly and insufficient)-induced ecological harms, using alternative additives in CMB has become essential. This study aims to increase the short-/long-term filling performance and to reduce cement-related costs by using both sand as tailings substitute, and GBS or FA (granulated blast furnace slag or fly ash) as OPC substitution. Some mechanical (UCS, stress-strain, and modulus of elasticity) and microstructural (MIP, XRD, TG/DTG and SEM) character-ization tests for CMBs were experimentally scrutinized. Samples were prepared at diverse curing ages (3-180 days), constant cement/solid content (5/72 wt%), three diverse aggregates (tailings/sand: 100/0, 90/10 and 70/ 30) and OPC (OPC/GBS-FA: 100/0, 90/10 and 70/30) substitution ratios. Results disclosed that 30% sand-based CMB (S30) offered the best strengths. Besides, strength loss was observed in all 90-day cured backfills, while strength gain was observed in sand/GBS-based backfills up to 180 days. This can be stated by the fact that sand/ GBS supports hydration reactions and prevent fill acidifying in the long-term owing to their high CaO contents (sand:-54%; GBS:-35%). Moreover, improving sand's gradation, filling the voids of fine-grained GBS and FA is one of the cogent reasons for strength gains. To summarize, this study runs a full report on a cost-effective and viable CMB system that will both make operations profitable/sustainable and prevent environmental damages.